The present invention is directed to a method and apparatus for stabilizing adjacent bones, and is particularly directed to a method and apparatus for attaching and stabilizing adjacent vertebral bodies while the vertebral bodies fuse together.
Each adjacent pair of vertebrae in the human spinal column are separated by an intervertebral disc that makes relative movement of the vertebrae possible. Problems, however, can develop with one or more of the discs, causing severe back pain. In some cases, it is necessary to remove a problematic disc and to fuse the adjacent vertebrae together in order to relieve pain.
One known method for fusing an adjacent pair of vertebrae following removal of a disc is to implant a device, commonly referred to as a fusion cage, into the interbody space where the disc was removed. The fusion cage facilitates fusion of the vertebrae. Typically, procedures such as reaming and/or tapping of adjacent vertebrae are required to prepare the adjacent vertebrae to receive the fusion cage. Such procedures normally involve substantial cutting of the hard cortical bone of the end plates of the adjacent vertebrae, which can weaken the end plates and lead to collapse of the vertebrae. The fusion cage is then positioned in the interbody space and into engagement with the adjacent vertebrae. At least one known fusion cage has relatively movable parts that enable the fusion cage to be expanded after the fusion cage is positioned in the interbody space between adjacent vertebrae. The design of this expandable fusion cage is, however, relatively complex.
Typically, a fusion cage includes an internal cavity that is filled with bone graft material. The fusion cage and the bone graft material promote bone growth that slowly unites the adjacent vertebrae. The typical fusion cage, while in engagement with the adjacent vertebrae, does not attach to the vertebrae and thus does not resist relative movement of the vertebrae, through bending or rotation, along any one of the three planes of motion (sagittal, coronal, or horizontal). Rather, the typical fusion page relies on the viscoelasticity of the surrounding ligaments to stabilize the adjacent vertebrae.
It is desirable to provide an apparatus for implantation into an adjacent pair of vertebral bodies that attaches to and thus fastens the vertebral bodies while they fuse together despite the forces on the apparatus from human body movement and muscle memory. It is further desirable to provide an apparatus which has a simple one-piece construction and which may be implanted into an adjacent pair of vertebrae without having to prepare the adjacent vertebrae to accept the apparatus by substantial cutting of the cortical bone.
The present invention is an apparatus for implantation into an adjacent pair of vertebral bodies having first and second surfaces that oppose each other. The apparatus, when implanted, is attached to the adjacent pair of vertebral bodies and stabilizes the vertebral bodies while the vertebral bodies fuse together. The apparatus comprises a platform having a third surface extending transverse to the first and second surfaces. The apparatus further comprises at least one helical spike for embedding into each of the adjacent pair of vertebral bodies upon rotation of the platform to attach the at least one helical spike to each of the vertebral bodies and thus fasten (pin) the vertebral bodies together. The at least one helical spike projects from the platform and extends around a longitudinal axis. The at least one helical spike has a tip portion at a distal end for penetrating the first and second surfaces and for screwing into the adjacent pair of vertebral bodies as the platform is rotated. The at least one helical spike at least partially defines an internal cavity for receiving material that promotes fusion of the vertebral bodies.
In accordance with one embodiment of the present invention, the apparatus comprises a pair of helical spikes. The proximal ends of the pair of helical spikes are spaced 180xc2x0 apart.
In accordance with another embodiment of the present invention, the apparatus comprises three helical spikes extending around the longitudinal axis. The proximal ends of the three helical spikes are spaced 120xc2x0 apart.
The present invention also provides a method for attaching and stabilizing an adjacent pair of vertebral bodies while the vertebral bodies fuse together, the vertebral bodies having first and second surfaces that oppose each other. The method comprises the step of removing disc material disposed between the vertebral bodies to create an interbody space and the step of providing an interbody stabilizer for insertion into the interbody space by implanting the interbody stabilizer into both of the adjacent pair of vertebral bodies. The interbody stabilizer comprises a platform and at least one helical spike. The platform has a third surface extending transverse to the first and second surfaces of the vertebral bodies. The at least one helical spike projects from the platform and extends around a longitudinal axis. The at least one helical spike at least partially defines an internal cavity for receiving material that promotes fusion of the vertebral bodies. The method further comprises the step of embedding the interbody stabilizer into each of the adjacent pair of vertebral bodies by rotating the platform of the interbody stabilizer. Rotation of the platform causes the at least one helical spike to penetrate into and subsequently out of each of the vertebral bodies in an alternating manner to attach the interbody stabilizer to each of the vertebral bodies and thus fasten (pin) the vertebral bodies together. Material that promotes fusion of the vertebral bodies is placed into the internal cavity in the interbody stabilizer.